Drag block assembly

ABSTRACT

Disclosed is a drag block assembly for use with a downhole tool in a subterranean well, such as packers or bridge plugs. The drag block assembly comprises a generally cylindrically shaped sleeve and a block element. The block element is mounted to the sleeve such that it can radially slide. The block element is outwardly biased from the sleeve by an electromagnetic element.

FIELD

This disclosure relates to drag block assemblies for use with downhole tools in subterranean wells, such as packers or bridge plugs.

BACKGROUND

In the completion and the production of hydrocarbons from wells, it is frequently necessary to isolate a portion of the well using a well tool, such as a packer, plug, tubing hanger and the like, supported in the wellbore at a subterranean location. These tools are lowered into the well in a retracted state called the “run position”; and in a process called “setting”, the gripping means and packing means are radially expanded to a “set position” wherein the slips means and packing means engage the wellbore. A variety of types of gripping means are well known in the art, such as a slip means with wedge-shaped slip elements. Typically, packing means have resilient annular members mounted on the tool to move axially to pack off or seal the annulus around the tool. Such packing means can comprise one or more resilient annular packing elements which, depending on the use environment, may also comprise back up and/or anti-extrusion rings. When these packing elements are axially compressed, they expand radially from the mandrel into contact with the wellbore. To hold these tools in place in the wellbore against movement, slip means typically are mounted on the tool. These slip means, like the packing means, expand radially to grip the wellbore when forced to compress axially.

Axially directed forces are used to axially compress the packing elements and slip assemblies. Such forces are typically generated by moving the tubing string, initiating an explosive charge, or applying pressure to the tool. Examples of tools that are set by manipulating the tubing string include weight down and tension packers. A weight down packer is one in which force generated by the weight of the tubing string above the tool is used to set (expand) the packing and slip element and to hold the tool in set condition. In a tension packer, the tubing string is placed in tension and that tension force is used to set and hold the tool in the set condition.

Weight down and tension packers typically comprise a hollow tubular mandrel which is connected to the tubing string. Mounted on the mandrel are the axially compressible packing elements adjacent to the slip assembly. An annular tool element called a “drag block assembly” is located on the mandrel, adjacent the slip assembly on the opposite side from the packing elements. In weight down tools, the drag block is located below the slip means. In a tension packer, the drag block is located above the slip means.

Drag block assemblies typically frictionally engage the wellbore. Drag block assemblies are mounted to slide axially on the mandrel. Drag block assemblies are used to center the tool in the middle of the casing and to provide a resistant force or frictional force, which aids in the rotating, setting and unsetting of downhole tools. This frictional force is also referred to as “drag friction”.

Conventional prior art packers use drag block having leaf, bow or compression springs to provide a resistant force pushing the drag block against the interior surface of the casing thus creating friction between the drag block and the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a drag block assembly in accordance with an embodiment.

FIG. 2 is a perspective view of a drag block element usable in the drag block assembly of FIG. 1.

FIG. 3 is a schematic cross-sectional view of a drag block mounted in the sleeve of the drag block assembly of FIG. 1.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numbers are used herein to designate like elements throughout the various views, various embodiments are illustrated and described. The figures are not necessarily drawn to scale; and in some instances, the drawings have been exaggerated and/or simplified in places for illustrative purposes only. In the following description, the terms “upper,” “upward,” “lower,” “below,” “downhole” and the like, as used herein, shall mean: in relation to the bottom or furthest extent of the surrounding wellbore even though the well or portions of it may be deviated or horizontal. The terms “inwardly” and “outwardly” are directions toward and away from, respectively, the geometric center of a referenced object. Where components of relatively well-known designs are employed, their structure and operation will not be described in detail. One of ordinary skill in the art will appreciate the many possible applications and variations of the present invention based on the following description.

Turning now to FIG. 1, a drag block assembly 10 in accordance with one embodiment can be seen. Drag block assembly 10 comprises a generally cylindrically shaped sleeve 20 and a block element 40. Sleeve 20 can be suitable for being received on a mandrel 12. Mandrel 12 can be attached to a downhole tool at upper end 14 and/or lower end 16, or mandrel 12 can be part of a mandrel of a downhole tool. Mandrel 12 has a longitudinal central axis or longitudinal axial centerline 18. Also, as referred to herein, the term “radially” will refer to a radial direction perpendicular to the longitudinal axial centerline 18 and “longitudinal” or “axial” will refer to a direction parallel to the longitudinal axial centerline 18.

Referring now to FIGS. 1 and 3, sleeve 20 has an outer surface 22, an array of longitudinally disposed slots 24 disposed around outer surface 22, and an inner surface 26 at the bottom of each slot 24. A wall 28 extends from inner surface 26 to outer surface 22 in each slot 24. A first magnet 30 is mounted in inner surface 26; thus, there are a plurality of magnets disposed about sleeve 20 in the bottom of slots 24. First magnet 30 can be embedded within a channel 34 in inner surface 26 such that the outer surface 32 of first magnet 30 lies flush with inner surface 26. Typically, first magnet 30 will be an elongated magnet having a length at least 50% of the length of slot 24 and can be at least 70 percent of the length of slot 24. The width of first magnet 30 will generally be from 80% to 100% of the width of slot 24. Alternatively, first magnet 30 can be a set of smaller magnets embedded into inner surface 26, as long as they align with the magnets in the block element to create a repulsive effect, as further described below.

Referring now to FIGS. 1, 2 and 3, a block element 40 is mounted to sleeve 20 such that it can radially slide. Block element 40 comprises an elongated block-like body 42 with a casing-wall-contacting outer surface 44 and a bottom surface 46. Further, a second magnet 48 is mounted in bottom surface 46. Typically, there are a plurality of block elements 40, such that each slot 24 has one of block elements 40 mounted in it with casing-wall-contacting outer surface 44 protruding through the slot and bottom surface 46 facing inner surface 26 of sleeve 20. Second magnet 48 is generally mounted flush in bottom surface 46. Typically, second magnet 48 is approximately the same size and shape as first magnet 30 and is positioned such that when block element 40 is mounted in slot 24, first magnet 30 and second magnet 48 will be aligned so as to generate a magnetic repulsion between the two magnets. Second magnet 48 can be mounted in a channel 49 in bottom surface 46 such that it is flush with bottom surface 46. Alternatively, both slot 24 and block element 40 can have several smaller magnets dispersed about inner surface 26 and bottom surface 46, as long as their positioning and magnetization generate a repelling force between the inner surface 26 and bottom surface 46. Also, while described in terms of magnets, other electromagnetic elements are within the scope of the invention as long as they produce a repelling electromagnetic force between inner surface 26 and bottom surface 46, such that casing-wall-contacting outer surface 44 of block element 40 is radially outwardly biased from sleeve 20 by the electromagnetic elements. If magnets are used, typically the first magnet and the second magnet can have a magnetization sufficient to provide a spring-like action to the block element and generate a drag force between the block element and a casing of a wellbore when the drag block assembly is introduce into the casing.

Block element 40 has a first lateral end 50 and a second lateral end 52, which extend laterally as opposed to axially or longitudinally. Block element 40 also has first longitudinal side 54 and second longitudinal side 56, which extend axially or longitudinally. A first flange 58 extends lengthwise from first lateral end 50 and a second end flange 60 extends lengthwise from second lateral end 52. Accordingly, block element 40 can be mounted within slot 24 by retaining members on sleeve 20 that interact with flanges 58 and 60 so as to prevent block element 40 from moving out of slot 24. Thus, first flange 58 can be retained by a retaining tab 38 connected to sleeve 20, and second flange 60 can be retained by a retaining ring 36 circumferentially disposed about outer surface 22 of sleeve 20. When so mounted, block element 40 will be pushed outward from inner surface 26 by magnetic forces so as to form a gap 62 between inner surface 26 and bottom surface 46. Gap 62 allows block element 40 to move inward towards inner surface 26 when there is an exterior force on outer surface 44 great enough to overcome the magnetic force. Moreover, as bottom surface 46 nears inner surface 26, the magnetic force repelling the two surfaces will increase requiring greater exterior force to overcome it. When the exterior force lessens, block element 40 will move outwardly so as to have a spring-like action.

For example, a drag block assembly, having a gap 62 of 1 inch when block element 40 is in its outer most position in slot 24, might use two opposing grade N52 magnets having a length of 6 inches, a width of 1 inch and a depth of 1 inch. The magnets for this drag block assembly will exert approximately 110 lbs with a 1 inch gap with the magnetic field between magnets being about 1,107 gauss and the permeance coefficient being 1.6. As the distance between the magnets is compressed and approaches contact between the magnet, the force can increase to approximately 300-400lbs.

Drag block 40 can have an elastic member extending around its periphery, such as O-ring 64. When drag block 40 is mounted in slot 24, O-ring 64 contacts wall 28 to block debris from entering into gap 62. O-ring 64 is formed from an elastomeric material, such as Nitrile Butadiene Rubber (NBR). Mandrel 12 and sleeve 20 typically can be formed from a drillable material such as brass or composite materials such as engineered plastics. Specific plastics include nylon, phenolic materials and epoxy resins. Drag block element 40 can also be formed from a composite material or can be molded from an elastomeric material.

In operation, a plurality of block elements 40 are mounted in slots 24 spaced about the periphery of sleeve 20. Drag block elements 40 are outwardly biased within the slots by an electromagnetic element, such as magnet pairs 30 and 48. The resulting drag block assembly is mounted on a mandrel of a downhole tool. Next, the downhole tool is placed into a casing in a wellbore such that casing-wall-contacting outer surface 44 of each block element 40 presses outward on the casing, thus centering the downhole tool in the casing and creating drag friction. To provide additional drag force and to limit damage to block element 40, wear members 66 in the form of buttons or inserts can be mounted on or in casing-wall-contacting outer surface 44. The wear members can be formed from tough wear resistant materials, such as composite materials (hard rubber, resins and the like), metallic materials (steel, carbide and the like), and ceramic materials.

In accordance with the above description, there is provided in one embodiment a drag block assembly for a downhole tool. The drag block assembly comprises a generally cylindrical shaped sleeve and a block element. The block element is mounted to the sleeve such that it can radially slide. The block element is outwardly biased from the sleeve by an electromagnetic element. The electromagnetic element can comprise a first magnetic member mounted to the sleeve and a second magnetic member mounted to the block element. The first magnetic member and second magnetic member have magnetization aligned such that they repel each other. The first magnetic member and the second magnetic member can have a magnetization sufficient to provide a spring-like action to the block element and generate a drag force between the block element and a casing of a wellbore when the drag block assembly is introduce into the casing.

In a further aspect, the sleeve can have an outer surface, an array of longitudinally disposed slots disposed around the outer surface, and an inner surface at the bottom of each slot. The block element can have an elongated block-like body with a casing-wall-contacting outer surface and a bottom surface. There can be a plurality of the block elements, and each slot has one of the block elements mounted in it such that the casing-wall-contacting outer surface protrudes through the slot and the bottom surface faces the inner surface of the sleeve. The drag block can be radially moveable in the slot.

Further, the sleeve can comprise a wall extending from the inner surface to the outer surface in each slot. The block can have an elastic member extending around its periphery, such that the elastic member contacts the wall to block debris from entering into a space between the inner surface and the bottom surface.

Additionally, the electromagnetic element comprises a plurality of first magnetic members and second magnetic members. Each slot has one of said first magnetic members mounted to the inner surface thereof. Each block element has one of said second magnetic members mounted to the bottom surface thereof. The first magnetic member and the second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias the drag block element in the slot.

In another aspect, the block element can have a first lateral end having a first flange extending lengthwise therefrom and a second lateral end having a second flange extending lengthwise therefrom. The first flange can be retained by a retaining ring disposed about the outer surface of the sleeve, and the second flange can be retained by a tab connected to the sleeve. The block is thus mounted in and retained from moving out of the slot.

In another embodiment, there is provided a method of centering a downhole tool with drag friction. The method comprises:

-   -   (a) connecting a drag block assembly to the downhole tool, the         drag block assembly having a generally cylindrically shaped         sleeve and a plurality of block elements mounted to the sleeve         such that they can radially slide;     -   (b) biasing each block element outwardly from the sleeve by an         electromagnetic element; and     -   (c) placing the downhole tool into a casing in a wellbore such         that a casing-wall-contacting outer surface of each block         elements presses outward on the casing, thus centering the         downhole tool in the casing and creating drag friction.

In the method, the block elements are radially moveable. The electromagnetic element can comprise a plurality of first magnetic members mounted to the sleeve and a plurality of second magnetic members. Each block element has one of the second magnetic members mounted to it. The first magnetic member and second magnetic member have magnetization aligned such that they repel each other. Also, the sleeve can comprise an outer surface, an array of longitudinally disposed slots disposed around the outer surface, and an inner surface at the bottom of each slot. Each block element can comprise an elongated block-like body with a casing-wall-contacting outer surface and a bottom surface. Each slot can have one of the block elements mounted in it such that the casing-wall-contacting outer surface protrudes through the slot, and the bottom surface faces the inner surface of the sleeve. The sleeve can further comprise a wall extending from the inner surface to the outer surface in each slot. Each block can have an elastic member extending around its periphery, such that the elastic member contacts the wall to block debris from entering into a space between the inner surface and the bottom surface. The drag block can be radially moveable within the slot.

While various embodiments of the invention have been shown and described herein, modifications may be made by one skilled in the art without departing from the spirit and the teachings of the invention. The embodiments described here are exemplary only and are not intended to be limiting. Many variations, combinations, and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow. The scope includes all equivalents of the subject matter of the claims. 

What is claimed is:
 1. A drag block assembly for a downhole tool comprising: a generally cylindrically shaped sleeve; and a block element mounted to said sleeve, such that said block element can radially slide, and wherein said block element is outwardly biased from said sleeve by an electromagnetic element.
 2. The drag block assembly of claim 1, wherein said electromagnetic element comprises a first magnetic member mounted to said sleeve and a second magnetic member mounted to said block element, and wherein said first magnetic member and second magnetic member have magnetization aligned such that they repel each other.
 3. The drag block of claim 2, wherein said first magnetic member and said second magnetic member have a magnetization sufficient to provide a spring-like action to said block element and generate a drag force between said block element and a casing of a wellbore when said drag block assembly is introduce into said casing.
 4. The drag block assembly of claim 1, wherein: said sleeve has an outer surface, an array of longitudinally disposed slots disposed around said outer surface, and an inner surface at the bottom of each slot; said block element has an elongated block-like body with a casing-wall-contacting outer surface and a bottom surface; and there are a plurality of said block elements, each said slot has one of said block elements mounted in said slot such that said casing-wall-contacting outer surface protrudes through said slot, and said bottom surface faces said inner surface of said sleeve.
 5. The drag block assembly of claim 4, wherein: said sleeve further comprises a wall extending from said inner surface to said outer surface in each slot; and said block has an elastic member extending around its periphery, such that said elastic member contacts said wall to block debris from entering into a space between said inner surface and said bottom surface.
 6. The drag block assembly of claim 4, wherein said drag block is radially moveable within said slot.
 7. The drag block assembly of claim 6, wherein said electromagnetic element comprises a plurality of first magnetic members and a plurality of second magnetic members, said inner surface of each said slot has one of said first magnetic members mounted thereto, said bottom surface of each block element has one of said second magnetic members mounted thereto, and wherein said first magnetic member and said second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias said drag block element in said slot.
 8. The drag block assembly of claim 4, wherein said block element has a first lateral end having a first flange extending lengthwise therefrom and a second lateral end having a second flange extending lengthwise therefrom and wherein said first flange is retained by a retaining ring disposed about said outer surface of said sleeve and said second flange being retained by a tab connected to said sleeve wherein said block is thus mounted in and retained from moving out of said slot.
 9. The drag block assembly of claim 8, wherein said drag block is radially moveable within said slot.
 10. The drag block assembly of claim 9, wherein: said sleeve further comprises a wall extending from said inner surface to said outer surface in each slot; and said block has an elastic member extending around its periphery such that said elastic member contacts said wall to block debris from entering into a space between said inner surface and said bottom surface.
 11. The drag block assembly of claim 10, wherein said electromagnetic element comprises a plurality of first magnetic members and a plurality of second magnetic members, said inner surface of each said slot has one of said first magnetic members mounted thereto, said bottom surface of each block element has one of said second magnetic members mounted thereto, and wherein said first magnetic member and said second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias said drag block element in said slot.
 12. The drag block of claim 11, wherein said first magnetic member and said second magnetic member have a magnetization sufficient to provide a spring-like action to said block element and generate a drag force between said block element and a casing of a wellbore when said drag block assembly is introduce into said casing.
 13. A method of centering a downhole tool with drag friction comprising: (a) connecting a drag block assembly to said downhole tool, said drag block assembly having a generally cylindrically shaped sleeve and a plurality of block elements mounted to said sleeve such that they can radially slide; (b) biasing each said block element outwardly from said sleeve by an electromagnetic element; and (c) placing said downhole tool into a casing in a wellbore such that a casing-wall-contacting outer surface of each block elements presses outward on the casing thus centering the downhole tool in the casing and creating drag friction.
 14. The method of claim 13, wherein said electromagnetic element comprises a plurality of first magnetic member mounted to said sleeve and a plurality of second magnetic member, wherein said first magnetic members are mounted to said sleeve, each said block element has one of said second magnetic members mounted thereto, and said first magnetic member and second magnetic member have magnetization aligned such that they repel each other.
 15. The method of 14, wherein said first magnetic member and said second magnetic member have a magnetization sufficient to provide a spring-like action to said block element and generate a drag force between said block element and said casing when said drag block assembly is introduce into said casing.
 16. The method of claim 15, wherein: said sleeve comprises an outer surface, an array of longitudinally disposed slots having a bottom and disposed around said outer surface, and an inner surface at said bottom of each slot; each said block element comprises an elongated block-like body with a casing-wall-contacting outer surface and a bottom surface; and each said slot has one of said block elements mounted in said slot such that said casing-wall-contacting outer surface protrudes through said slot, and said bottom surface faces said inner surface of said sleeve.
 17. The method of claim 16, wherein: said sleeve further comprises a wall extending from said inner surface to said outer surface in each slot; and said block has an elastic member extending around its periphery such that said elastic member contacts said wall to block debris form entering into a space between said inner surface and said bottom surface.
 18. The method of claim 17, wherein said electromagnetic element comprises a plurality of first magnetic members and a plurality of second magnetic members, said inner surface of each said slot having one of said first magnetic members mounted thereto, said bottom surface of each said drag block element having one of said second magnetic members mounted thereto, and wherein said first magnetic member and said second magnetic member have magnetization aligned such that they repel each other to thus outwardly bias said drag block element in said slot.
 19. The method of claim 18, wherein said drag block is radially moveable within said slot. 